Their fellow Americans Jake Gibb and Sean Rosenthal followed them on court and beat a Russian pair on a beautiful night at Horse Guards Parade, a venue in the heart of the city where the London Eye lights up the sky.
It was a sweet night for the United States after their men's defending Olympic champions Todd Rogers and Phil Dalhausser were knocked out by Italians Daniele Lupo and Paolo Nicolai on Friday in the biggest upset of the tournament.
The only pair of either gender to have successfully defended an Olympic title, May-Treanor and Walsh made fast work of Marleen van Iersel and Sanne Keizer, beating them by two sets to nil (21-13, 21-12) in half an hour.
"We wanted to force them to make errors and I think we did a good job," said May-Treanor, stating a fact rather than an opinion. She was wearing a delicate gold necklace with a beach volleyball logo and the Olympic rings, a gift from her coach in Beijing, where she and Walsh won their second gold in 2008.
"It's sudden elimination and anything can happen. Both of us have large targets on our backs. Two-time Olympic gold medallists, everybody wants to take you down. But that makes us work harder."
Walsh, who is 1.88 metres tall, proved an insurmountable obstacle for the Dutch. When they tried to power past her with spikes, their balls would come right back at them, and when they tried to go over her, their balls would go out of the court.
Anything that did go over the net fell into the deft hands of May-Treanor, who makes up for her relative lack of height with versatility in both attack and defence, constantly confusing her opponents with her unpredictable shots.
In the quarter-finals, May-Treanor and Walsh will face Italians Greta Cicolari and Marta Menegatti, who are considered the strongest European women's pair in a sport dominated by Americans and Brazilians.
Gibb and Rosenthal breezed through their first set against Russia's Konstantin Semenov and Serguei Prokopiev, winning it 21-14, but the Russians pushed them harder in the second set.
The Americans held their nerve to win it 22-20.
The first two sets are usually played to 21 points but a two-point advantage is required to win.
The American-Russian clash ended the round-of-16. The women's quarter finals are on Sunday and the men's on Monday.
Earlier, German former world champions Julius Brink and Jonas Reckermann beat Latvians Ruslans Sorokins and Aleksandrs Samoilovs by two sets to nil (21-12, 21-17) to set up a tough quarter final against Brazilians Ricardo Santos and Pedro Cunha.
The experienced Germans, the 2009 world champions, are in a stronger-than-expected position after their side of the draw was opened up when Rogers and Dalhausser crashed out on Friday.
But they will have their work cut out for them against Ricardo and Cunha. Ricardo is in his fourth Olympics, having won medals in the three previous Games with two former partners. He was a gold medallist with Emanuel Rego in Athens in 2004.
Emanuel is also competing in London with his new team mate, Alison Cerutti, and the pair are the reigning world champions.
They were in action earlier on Saturday, easily beating another German pair, Jonathan Erdmann and Kay Matysik, by two sets to nil (21-16, 21-14).
In the women's event, medal contenders Zhang Xi and Xue Chen scored an easy win over Russia's Evgenia Ukolova and Ekaterina Khomyakova, recovering their confidence after unexpectedly losing their first pool match against another Russian pair.
"We found our own style and our own tactics. We didn't change the way we play for the Russians, we just played our own way," said Xue after the pair won by two sets to nil with the emphatic score of 21-12, 21-11.
Zhang and Xue were surprise bronze medallists in Beijing in 2008 and have come to London with high expectations. The other favourites among the women's pairs are May-Treanor and Walsh on the one hand, and Juliana Felisberta and Larissa Franca of Brazil on the other.
Juliana and Larissa are the reigning world champions. They were unable to play together in Beijing because Juliana had a knee injury, and are intent on making up for that in London.
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